Functionalization of halloysite nanotubes with polyethyleneimine and various ionic liquid forms with antimicrobial activity

Fe3O4-Halloysite Nanotube Composites as Sustainable Adsorbents: Efficiency in Ofloxacin Removal from Polluted Waters and Ecotoxicity

The present work aimed at decorating halloysite nanotubes (HNT) with magnetic Fe₃O₄ nanoparticles through different synthetic routes (co-precipitation, hydrothermal, and sol-gel) to test the efficiency of three magnetic composites (HNT/Fe₃O₄) to remove the antibiotic ofloxacin (OFL) from waters. The chemical-physical features of the obtained materials were characterized through the application of diverse techniques (XRPD, FT-IR spectroscopy, SEM, EDS, and TEM microscopy, thermogravimetric analysis, and magnetization measurements), while ecotoxicity was assessed through a standard test on the freshwater organism Daphnia magna. Independently of the synthesis procedure, the magnetic composites were successfully obtained. The Fe₃O₄ is nanometric (about 10 nm) and the weight percentage is sample-dependent. It decorates the HNT's surface and also forms aggregates linking the nanotubes in Fe₃O₄-rich samples. Thermodynamic and kinetic experiments showed different adsorption capacities of OFL, ranging from 23 to 45 mg g^-1. The kinetic process occurred within a few minutes, independently of the composite. The capability of the three HNT/Fe₃O₄ in removing the OFL was confirmed under realistic conditions, when OFL was added to tap, river, and effluent waters at µg L^-1 concentration. No acute toxicity of the composites was observed on freshwater organisms. Despite the good results obtained for all the composites, the sample by co-precipitation is the most performant as it: (i) is easily magnetically separated from the media after the use; (ii) does not undergo any degradation after three adsorption cycles; (iii) is synthetized through a low-cost procedure. These features make this material an excellent candidate for removal of OFL from water.

Silver nanoparticle@carbon quantum dot composite as an antibacterial agent

Synthesis of AgNPs@S,N-CQDs active against bacteria.

Multifunctional polyethylene imine hybrids decorated by silica bioactive glass with enhanced mechanical properties, antibacterial, and osteogenesis for bone repair

Inorganic/organic hybrids and bioactive glasses demonstrate promising potential as bone substitute biomaterials. A sol-gel hybrid consisting of silica bioactive glass and biodegradable polymer can combine the high bioactivity of a glass with the toughness of a polymer. In this study, multifunctional hybrids with a combination of organic-inorganic hybrid structure class II consisting of polyethyleneimine (PEI) generation 4 (G4) and bioactive glass with enhanced mechanical properties, mineralization, antibacterial, and osteogenesis activities were synthesized by the sol-gel method. Glycidoxypropyl) trimethoxysilane (GPTMS) with different concentrations was used as a covalent bonding agent between PEI polymer and bioactive glass. The effect of GPTMS content was assessed in the presence and absence of calcium in the hybrid structures in terms of morphology, wettability, mechanical properties, antibacterial activity, cell viability, and in vitro osteogenic differentiation properties. By increasing the amount of GPTMS, the compressive strength increased from 1.95 MPa to 2.34 MPa, which was comparable to human trabecular bone. All the hybrids presented antibacterial activity against Staphylococcus aureus, forming an inhibition zone of 13-16 mm. An increase in cell viability of 82.22% in PSCaG90 was obtained after 1 day of MG-63 cell culture. Alkaline phosphatase expression and mineralization of MG-63 cells increased in the PSCaG90 hybrid in the absence of an osteogenic medium compared to PSG60 and PSG90. The PSCaG90 hybrid indicated considerable in vitro osteogenic capacity in the absence of a differentiation medium, expressing high levels of bone-specific proteins including collagen I (COL1A1), Runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN), compared to calcium-free hybrids. Overall, our results suggest that the presence of calcium in the PSCaG90 leads to a significant increase in osteogenic differentiation of MG-63 cells even in the absence of differentiation medium, which suggests these hybrid structures with multifunctional properties as promising candidates for bone repair.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

Antimicrobial dressing of silver sulfadiazine-loaded halloysite/cassava starch-based (bio)nanocomposites

(Bio)nanocomposites have been studied for biomedical applications, including the treatment of wounds. However, wound infection is one of the main problems of wound care management, and the use of wound dressings with antibacterial agents is essential. This work focused on developing and characterizing silver sulfadiazine-loaded halloysite/cassava starch-based (bio)nanocomposites potentially suitable as antimicrobial dressing. Silver sulfadiazine was complexed inside the halloysite nanotubes lumen, and the drug-loaded nanotubes were incorporated in thermoplastic starch dispersion, forming the (bio)nanocomposites. The silver sulfadiazine-loaded halloysite and the (bio)nanocomposite were characterized by zeta potential, scanning electron microscopy, X-ray diffraction, and infrared spectroscopy. The dressing properties of (bio)nanocomposites (water vapor permeability and mechanical stability) and their antimicrobial efficacy by Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were also evaluated. Physicochemical studies suggested the silver sulfadiazine-loaded halloysite complexation (zeta potential of -38.9 mV) and its interactions with the starch forming the nanocomposites. The silver sulfadiazine-loaded halloysite/starch-based (bio)nanocomposites possessed a homogeneous and organized structure. Also, they had mechanical properties to be used as a dressing (13.73 ± 3.09 MPa and 3.17 ± 1.28% of elongation at break), and its permeability (6.18 ± 0.43 (10^-13) g.Pa^-1.s^-1.m^-1) could be able to maintain the environmental moisture at the wound surface. Besides that, the (bio)nanocomposites acted against the studied bacteria, being a potential contact antimicrobial and biodegradable wound dressing. Finally, the developed (bio)nanocomposites are semi-occlusive and good candidates for dry wounds to be widely in vitro and in vivo tested as controlled silver sulfadiazine delivery dressing.

Synthesis, characterization and investigation of synergistic antibacterial activity and cell viability of silver-sulfur doped graphene quantum dot (Ag@S-GQDs) nanocomposites

The excessive use of traditional antibiotic and antibacterial agents has globally increased the growth of antibiotic-resistant bacteria that poses serious health risks. Therefore, the development of new generation antibacterial or antimicrobial agents for effective inhibition of bacterial growth is highly desired. In this study, we report a facile one-step synthesis approach for the preparation of a nanocomposite composed of silver nanoparticles (AgNPs) decorated with sulfur-doped graphene quantum dots (S-GQDs). The nanocomposite was comprehensively characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectra, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrated that the AgNPs were closely and uniformly surrounded by the S-GQDs, and consequently, this ensured the dispersion and stability of the so formed nanocomposite (Ag@S-GQDs). Further, the antibacterial activity of the Ag@S-GQDs nanocomposite was investigated and compared with bare S-GQDs and AgNPs against Gram-positive S. aureus (MTCC 737) and Gram-negative P. aeruginosa (MTCC 424) bacteria using macrodilution and agar well diffusion methods. Minimum inhibitory concentration (MIC) values of 70 and 35 μg mL^-1 of the Ag@S-GQDs nanocomposite were found to be sufficient to hinder the growth of P. aeruginosa and S. aureus. A fractional inhibition concentration (FIC) index below 0.5 confirmed the existence of a synergistic effect between AgNPs and S-GQDs in the Ag@S-GQDs nanocomposite. In addition, the cytotoxicity of the Ag@S-GQDs nanocomposite, AgNPs and S-GQDs was also investigated using HEK 293 cell lines. Interestingly, the Ag@S-GQDs nanocomposite exhibited superior cell viability as compared to AgNPs and S-GQDs. These improved antibacterial and biocompatibility data demonstrate that the Ag@S-GQDs nanocomposite can serve as a promising antibacterial agent for industry to fabricate next-generation self-sterile textiles, antibacterial coatings and useful health care products supporting cell viability.

Antimicrobial activity and biocompatibility of slow-release hyaluronic acid-antibiotic conjugated particles

Here, the aim was to design and use a long-lasting antibiotic release system for prevention of postoperative infections in ophthalmic surgery. Ciprofloxacin and vancomycin-conjugated hyaluronic acid (HA) particles were prepared as drug carriers for sustained release of antibiotics. The antimicrobial effects of the released drugs were determined by disc-diffusion and macro-dilution tests at different times up to 2 weeks. Slow degradable HA particles were obtained with 35.2 wt% degradation within 21 days. The drug loading amount was increased by employing two sequential chemical linking (conjugation, 2C) and one physical absorption loading (A) procedures (2C + A processes) from 148 ± 8 to 355 ± 11 mg/g HA particles for vancomycin. The amounts of vancomycin and ciprofloxacin that were released linearly was estimated as 64.35 ± 7.35 and 25.00 ± 0.68 mg/g, respectively, from drug-conjugated HA particles in 100 h. Antimicrobial studies revealed that antibiotic-conjugated HA particles could inhibit the growth of microorganisms from 1 h to 1 week. The MBC values were measured as 0.25, 4.0, and 0.25 mg/mL against Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis, respectively, after 72 h incubation time. Cytotoxicity studies showed no difference between fibroblast growth or corneal thickness after 5 days with or without HA-antibiotic particles. The drug release studies and antimicrobial activity of antibiotic-loaded HA particles with time against various bacteria further revealed that HA particles are very effective in preventing bacterial infections. Likewise, cytotoxicity studies suggest that these particles pose no toxicity to eukaryotic cells, including corneal endothelium.